These sounds make no echoes. UA researchers say that's important for cellphones and more
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When the cutting edges of math, science and engineering meet, things get weird: Light bends around corners; fabrics grow wider as you make them longer; doughnuts begin to look like coffee mugs.
In acoustics, researchers have spent decades working with strange forms and novel materials to bend and focus sound, advancing fields like cloaking and soundproofing.
“But over the past 10 years, there have been a recognition that we've been missing something in this research, and that there are attributes of acoustic waves that we've not focused on,” said University of Arizona professor Pierre Deymier.
Deymier is director and principal investigator of New Frontiers of Sound (NewFoS), a consortium with eight other universities: California Institute of Technology; the City University of New York; Georgia Institute of Technology; Spelman College in Atlanta; University of Alaska Fairbanks; University of California, Los Angeles; the University of Colorado Boulder; and Wayne State University in Detroit.
Together, they share a singular focus: “To research the potential applications of topological acoustics for many technologies: information processing, telecommunication or sensing.”
NewFoS has received $30 million in funding for its first five years with an option to apply for a five-year extension. After that, NSF expects its Science and Technology Centers to obtain other income sources.
Going through a phase
Topological acoustics (TA) deals a lot with an aspect of waves called phase. But it’s a bit weirder than the “phase” they talk about in trig class.
Imagine you’re in a furnished room. A speaker is playing music. Sound waves are bouncing around, creating a sound field — a pattern like waves on a rocky lake.
“So, let's suppose I rotate my source of sound by half a turn, then the room is filled with sound in a different manner, and I get a new sound field,” said Deymier.
You might think that another half-spin would return the speaker to its original facing and therefore restore its original sound field. But you’d be only half right. Because, under the rules of TA, you actually have to spin the speaker all the way around again to return to where you started.
“It sounds very strange, and it is indeed very strange,” said Deymier. “But it is one of the characteristics of topological acoustic waves.”
Tuning up the band
TA researchers also work with something called band structures, which have less to do with halftime shows and more with why some materials conduct energy while others insulate it.
Such structures are not confined to electricity, however: Phononic band gaps affect how materials to conduct or insulate sound.
“This arises from the unique properties of topologically engineered materials, so that the sound that goes in one direction cannot traverse back in the other direction; there's no echo,” said Keith Runge, director of knowledge transfer for NewFoS.
Using these band properties, experts can turn jangling mosh pits of interference into gliding ice rinks of transmission.
On the ice or in a ballroom, the outer ring progresses smoothly, unimpeded by beginners or dancers doing other steps.
And that dance lane moves in only one direction. That means no echo, which is a potential game changer for cellphones, for example, and the many acoustic filters they use to maintain call quality, signal strength and channel isolation.
“We eliminate the echo that will happen in such devices, and therefore we reduce the amount of power that is lost because of that echo,” said Deymier.
Taking it on the road
TA also has uses outside the lab. Together with University of Alaska Fairbanks, NewFoS is monitoring permafrost by sensing how the ground’s phase changes as it thaws.
“The only thing we have to do is pull up a number of seismic sensors and create a network of seismic sensors that are going to detect the phase of the seismic waves,” said Deymier.
But explorers are only as good as the maps they leave behind, which is why education is a major component of NewFoS. Leading that effort is Sara Chavarria, assistant dean for research development at UA.
She said initial efforts will focus on higher education, staff and researchers.
“We eventually want to also write additional grants to target K-12 teachers, but we want to really kind of get up and running as a center first,” she said.
Central to those efforts will be training in mentorship and creating inclusive spaces.
The center will also sponsor a 12-month research and mentoring program, beginning with an eight-week summer immersion.
“They work on a research project with the researchers, graduate students and postdocs in the laboratory,” said Chavarria.
NewFoS will provide funding to help attract and retain underrepresented students, many of whom traditionally have to work long hours to make ends meet before paying for schooling.
The center faculty and staff will also work with undergraduates to design a TA textbook and curriculum.
“I'm very excited about that one, because I love working with undergraduate students. They are very creative, and they're always translating in order to help each other out,” said Chavarria.
For now, it’s early days. In the nine years running up to its successful application, the NewFoS leadership has had ample time to refine its plans, hone its mission and publish its first paper.
“And I would be surprised and greatly disappointed if we didn't have some invention disclosures and patent applications in the first two or three years,” said Runge.
